Key Findings of the US Government’s Climate Science Special Report

Today, the US Global Climate Change Research Program released the Climate Science Special Report, Vol. 1 of the Fourth National Climate Assessment mandated by Congress to provide the latest scientific basis and impacts from climate change on the United States. Climate science continues to evolve, but in the direction of more significant realization of how humans have influenced the climate thus far, as well as how much more influence will come in the not to distant future.

Below are some of the headline findings provided in the rather powerful report (be prepared for a lot of INTENSE info):

    1. Earth’s average temperature has increased by 1 degree C (1.8 F) during the 1901-2016 period. This is faster than any rate known in the last 1,700 years.                 2017TempUpdate_Top10_Global_F_en_title_lg
    2. The average temperature of the contiguous United States has also increased by 1 degree C (1.8 F) during the 1901-2016 period. Satellite and surface observations are consistent in the detection of this rapid rise in temperature. With no change in the rate of greenhouse gas emissions, the CONUS is expected to experience a more abrupt average rise in temperature of 3.2-6.6 degrees C (5.8-11.9 F) between now and 2100.                                                                                 
      figure6_1
      Change in average surface temperature (annual and seasonal) for the period 1986-2016 since the period 1901-1960 (contiguous US; 1925-1960 for Alaska and Hawaii). Data from NOAA.

      figure6_8
      Projected changes in the coldest and warmest daily temperatures (°F) of the year in the contiguous United States. Changes are the difference between the average for mid-century (2036–2065) and the average for near-present (1976–2005) under the higher emissions scenario (RCP8.5). Maps in the top row depict the weighted multimodel mean whereas maps on the bottom row depict the mean of the three warmest models (that is, the models with the largest temperature increase). Maps are derived from 32 climate model projections that were statistically downscaled using the Localized Constructed Analogs technique. Increases are statistically significant in all areas (that is­­, more than 50% of the models show a statistically significant change, and more than 67% agree on the sign of the change). Data by NOAA.
    3. Temperature extremes in the United States are trending significantly toward record high temperatures over record low temperatures. This trend is expected to continue with the number of below freezing days also continuing to decline and days above 32 degrees C (90 F) continuing to rise.
      figure6_5
      Data by NOAA.

      figure6_9
      Projected changes in the number of days per year with a maximum temperature above 90°F and a minimum temperature below 32°F in the contiguous United States. Changes are the difference between the average for mid-century (2036–2065) and the average for near-present (1976–2005) under the higher scenario (RCP8.5). Maps in the top row depict the weighted multimodel mean whereas maps on the bottom row depict the mean of the three warmest models (that is, the models with the largest temperature increase). Maps are derived from 32 climate model projections that were statistically downscaled using the Localized Constructed Analogs technique. Changes are statistically significant in all areas (that is, more than 50% of the models show a statistically significant change, and more than 67% agree on the sign of the change).
    4. The global influence of natural variability is limited to small fraction of observed climate trends. Solar output and the Earth’s internal natural variability have contributed only marginally to the observed changes in the climate system over the past century. There is no convincing evidence for natural cycles in the observational record that could explain the changes in the climate system.                                                                                                                                                         
    5. Heavy precipitation events have increased across the US since 1901. The highest increase over the Northeast and the second highest increase over the Midwest.                                                                                                                                2017ClimateExtremes_Downpours_3_en_title_lg
    6. Northern Hemisphere spring snow cover, North American maximum snow depth and Western US snow-liquid equivalent have all declined since the early 20th century. At current rates of decline and assuming no change in water resource management, chronic, long-duration hydrological drought conditions are possible for portions of the United States by 2100.                                                                                                                                                                                               
    7. Global mean sea-level has risen 7-8 inches (~0.2 m) since 1900 with 3 of those inches since 1993. Relative to the year 2000 is very likely global mean sea-levels will rise up to 0.6 ft (0.18 m) by 2030, 1.2 ft (0.38 m) by 2050 and 4.3 ft (1.3 m)+ by 2100. A more rapid degradation of the West Antarctic Ice Sheet may mean physically possible sea level rise theoretically exceeding 8 ft (2.4 m) by 2100 (confidence is low on this).                                                                                                                2016StateOfClimate_SLR_en_title_lg
    8. The global ocean has absorbed more than 93% of the heat caused by global warming since the mid-20th century. The oceans have warmed by about 0.7 degrees C (1.3 F) during the 1900-2016 period. Assuming no emissions changes, warming of the oceans by an average of 2.7 degrees C (4.9 F) is expected by 2100.                                                                                                                                       2016StateOfClimate_HeatStorage_en_title_lg
    9. The global ocean continues to undergo rapid acidification because of dissolved carbon dioxide from atmospheric emissions. The rate of acidification is unparalleled in the past 66 million years (since the Cretaceous-Paleogene Impact Event). At the current rate, the pH of the global ocean may decline from its current average of 8.1 to as low as 7.8 by the end of the century. Seawater with pH <8 can be corrosive to shellfish, plankton and coral which depend on carbonate structures for their shells, backbones and skeletons. The greatest change in acidity will be in Arctic Ocean.

      figure13_5-1200
      Predicted change in sea surface pH in 2090–2099 relative to 1990–1999 under the higher scenario (RCP8.5), based on the Community Earth System Models–Large Ensemble Experiments CMIP5 (Figure source: adapted from Bopp et al. 2013 ).
    10. The Arctic is warming at a rate approximately twice as fast as the global average with a rapid decline in sea ice volume and extent since satellite observations began in 1979. At the current rate of warming, the Arctic Ocean will be effectively ice-free in the month of September by the 2040s.                       

      siv_annual_max_loss_and_ice_remaining
      Arctic Sea Ice Volume since 1979. Note gradual and accelerating collapse of sea ice volume. Arctic may fall below 1,000 cubic kilometers at some point in the month of September in as early as several years to a decade or so. This will happen when the yearly sea ice maximum and loss of what remains equal.
    11. Global warming has contributed “significantly” to ocean-atmosphere variability in the North Atlantic Ocean; as a result these changes have contributed to the observed upward trend in North Atlantic hurricane activity since the 1970s. North Atlantic hurricanes are expected to increase in intensity (maximum sustained wind potential) with increasing precipitation rates during the 21st century.                                    2017Hurricanes_Info_en_title_lg

      figure9_2-1200
      Tracks of simulated Saffir–Simpson Category 4–5 tropical cyclones for (a) present-day or (b) late-21st-century conditions, based on dynamical downscaling of climate conditions from the CMIP5 multimodel ensemble (lower scenario; RCP4.5). The tropical cyclones were initially simulated using a 50-km grid global atmospheric model, but each individual tropical cyclone was re-simulated at higher resolution using the GFDL hurricane model to provide more realistic storm intensities and structure. Storm categories or intensities are shown over the lifetime of each simulated storm, according to the Saffir–Simpson scale. The categories are depicted by the track colors, varying from tropical storm (blue) to Category 5 (black; see legend). (Figure source: Knutson et al. 2015; © American Meteorological Society).
    12. Large forest fires in the Contiguous US and Alaska have increased since the early-1980s. This increase is expected to continue with “profound” impacts on ecosystems.                                                                                                                           2016Wildfires_temp_WEST_en_title_lg

Some other findings of note:

-For the period 1901-2016, the Dust Bowl Era (mid-1930s) remains the most extreme era for heat. This is thought to be largely the result of significant land-surface feedbacks caused by precipitation deficits and poor land management leading to reduced vegetation and strong surface heating (which in turn promoted further drying and land degradation). However, we are on a path to eclipse this period in US climate history in the coming decades, particularly as colder conditions (more found in 1930s winters for example) continue to decline in a warming climate and extreme heat continues to increase.

-The Climate report explains (as has been explained in previous scientific literature) the period of so-called “global cooling” which occurred from the mid-1940s to mid-1960s: aerosol particles generated by WWII and post-war industrial production (esp. coal power plants) which reflected some solar radiation into space temporarily slowing long-term global warming, even as carbon dioxide concentration in the atmosphere continued to increase.

-The report notes that annual precipitation has decreased over the West, Southwest and Southeast, while increases have occurred over the Plains, Midwest and Northeast. They specifically mention an increase in mesoscale convective systems (organized clusters of thunderstorms which dump significant rainfall) over the Plains and Midwest since 1979. Mesoscale convective systems are expected to increase in frequency and intensity during the 21st century.

-While tornado climatology related to climate change has been difficult to understand because of the reliability of storm reports before the 1990s, scientists involved in the report have concluded one interesting aspect…there is moderate confidence in a decrease in tornado days (day when tornadoes of any number are confirmed), as tornadoes are increasing on those days. Greater volatility in tornado occurrence year-to-year as well as a trend toward an earlier first occurrence during the year have been observed. Studies looking at the ingredients for severe storms with all modes of potential activity (tornadoes, hail, wind) suggest an increased frequency and intensity of severe storms over areas prone to them in the US in a warmer world, but confidence on details is low.

-This report concluded that observed drought and precipitation increases (1901-2016) cannot be confidently attributed human-induced global warming. The Dust Bowl Era remains the benchmark period for extreme drought conditions. However recent negative trends in soil moisture are believed to be attributable to warming temperatures. Although soil moisture projections in climate models are still considered in their “elementary” stages in the science, based on what is known, there appears to be a signal for further decreases in soil moisture over portions of the US (particularly West and Plains) by the end of this century, increasing the risk of chronic hydrological drought.

-I find the key finding #11 I listed particularly important. There has been much debate between scientists (particularly more observational minded meteorologists vs. climatologists) about whether there has been truly observable increase in N. Atlantic hurricane activity seasonally beyond the natural variability, given the limited period of reliable satellite record and intensity measurements. This statement is given MODERATE confidence given that global warming has caused increases in sea-surface temperatures, oceanic heat content and natural cycles on multi-annual and multidecadal time scales involve changes in not only these thermodynamic variables but also dynamic ones in response (vertical wind shear, position/intensity of monsoon troughs, development of tropical waves into organized TCs).

Additional Thoughts:

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Climate change will likely be one of the most difficult challenges the world will face this century (at least). Why? Why should we care?

When it comes to effects on people (which is what people care about), at the end of the day, what matters for the livelihood of people rich or poor? Food, water, living space. If these become challenged, you get human suffering (from economic to health threats) and geopolitical problems. The potential for significant drying and increasing chronic hydrologic droughts from loss of snowpack will lead to increasing populations in demand for resources seriously straining water resources. Crops around the world will face increasing difficulties from heat stress, prolonged droughts mixed with periods of more intense heavy rainfall events. Acidification and warming may threaten marine food resources already strained by overfishing around the world. Living space will become slowly threatened by sea level rise in low-lying areas and island nations…and more readily in the coming decades…by repeated far more extreme heat waves than previously in already hot, humid environments where cooling is not readily available, and possibly by diseases as ecosystems shift to different places, along with pests (which will also impact crops potentially).

Climate change isn’t just about warming, it’s about cascading impacts on the whole of the climate system. Without a drastic global shift to a low-carbon energy sources and the advancement of technology to remove carbon dioxide from the atmosphere, we are in store for a very challenging period in human history. This isn’t worse-case/best case or any of this. This is simply the path that we are on, no over-dramatic statements nor downplaying needed or tolerated. Hopefully we via our governments make the right choices.

–Meteorologist Nick Humphrey

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Five Year Anniversary of Landfall of Superstorm Sandy

Five years ago today (October 29, 2012), the post-tropical remnants of what was Hurricane Sandy made landfall on the New Jersey coastline as a hurricane-force windstorm, causing destructive straight-line winds and historic, damaging surge from the North Atlantic extending from the Jersey coast north into the New York City Metro Area, with historic flooding of lower Manhattan.

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Image of extremely large Hurricane Sandy by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite on October 28, 2012. Sandy would become the largest tropical cyclone on record in the North Atlantic Basin.
Sandy produced widespread wind gusts of 75-90 mph across portions of New York and New Jersey with heavy rainfall totals of 7-10 inches across parts of New Jersey, Delaware, and Maryland. Storm surge was Sandy’s main cause of significant damage, with wind damage and flooding rainfall additional impacts. The post-tropical “superstorm” caused a 10-13 ft storm surge which damaged and destroyed homes and businesses along the Jersey Shore and Hudson Waterfront, with a record 13.88 ft water rise reported at Battery Park in Lower Manhattan.

Damage_from_Hurricane_Sandy_to_house_in_Brooklyn,_NY
Damage by Super Storm Sandy in Brooklyn, NY (“Proud Novice” on Wikipedia).
1200px-121030-F-AL508-081c_Aerial_views_during_an_Army_search_and_rescue_mission_show_damage_from_Hurricane_Sandy_to_the_New_Jersey_coast,_Oct._30,_2012
Super Storm Sandy damage in Mantoloking, NJ taken on October 30, 2012. (US Air Force).
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The flooded Brooklyn-Battery subway tunnel in NYC on October 30, 2012 (“vcohen” on Wikipedia).
Sandy’s expansive storm surge was more intense by multiple factors. As it came poleward, it grew significantly in size, a typical phenomenon for tropical cyclones moving into the mid-latitudes. However, Sandy’s weakening and mid-latitude interactions caused it become the largest North Atlantic tropical cyclone on record, producing a huge fetch (extensive wind over long stretch of open water). This fetch allowed for the building of significant ocean waves and piling up of water toward the shallow continental shelf of the Atlantic coast of the US. And although Sandy weakened somewhat and became “non-tropical”, this did not matter as the very large wind field remained and forward momentum of the very heavy ocean could not settle down in time before pounding the coastline with destructive surge.

In addition, Sandy made landfall at high tide, enhancing the storm’s ability to flood dry land areas and cause direct damage with battering waves. I will also note that this “flood reach” was even greater because of climate change-induced sea level rise. Global sea levels have risen 9 inches since 1880 and while the Intergovernmental Panel on Climate Change (UN) continues to indicate a likely sea level rise of up to 3.2 ft by 2100, many other reputable scientists have suggested the possibility of multi-foot sea level rise occurring this century as the result of exponential glacial melt feedbacks in Greenland and Antarctica. Perhaps as high as 6.5-16.5 feet by 2100 (see references #1-2 below). This, of course would be catastrophic for vulnerable coastal cities for both livability but initially for any places already exposed to storm surges. New York City is one most at risk.


Sea level rise has also been locally enhanced along the Northeast US Coast because of abnormally warm waters building offshore for years, leading to increased thermal expansion of the water surface upward. This may also be a result of climate change-induced weakening (#3) of the Atlantic Meridional Overturning Circulation (AMOC). While Superstorm Sandy wasn’t “caused” by climate change, it was part of an increasing regime of more extreme weather events (and events with with more extreme hazard variables) and a prelude to what will be far more frequent in the coming decades.

Sandy was retired after the 2012 Hurricane Season, causing 233 deaths from the Caribbean to the United States and producing an incredible $75 billion in damages (only 2nd to Hurricane Katrina). An incredible and devastating meteorological event which we can hope we continue to recover from and our country will be better prepared to mitigate against next time.

ussatsfc2012102921
Surface analysis at 5 pm EDT October 29, 2012 showing Superstorm Sandy just offshore the coast of New Jersey pounding the Mid-Atlantic to New England. The intense pressure gradient (shown by the isobars) caused areas of gale and storm force winds over the Great Lakes because of the expanse of the storm.
Scientific References (for the nerds like me!):

1- Hansen et al. 2016. (scientific technical)

2- New science suggests the ocean could rise more — and faster — than we thought (Washington Post/Oct 17)

3. Youtube video of conference presentation (2016) by Dr. Stefan Rahmstorf on weakening AMOC. Can also refer to (#1) on this issue as it relates to potential effect on ice sheet dynamics.

Hurricane Ophelia now a very rare Category 3 storm south of Azores

Hurricane Ophelia has strengthened into a Category 3 hurricane with maximum sustained winds of 115 mph as it moves south of the Azores. It is moving over prime atmospheric conditions, even as it overcomes waters of only 25 degrees C/77 degrees F. In normal tropical environments, tropical cyclones need water temperatures of 26 degrees C/79 degrees F to maintain themselves and warmer to significantly strengthen. However, the colder temperatures in the upper-atmosphere associated with the mid-latitude troposphere is providing Ophelia with ample atmospheric instability (warm, moist air rising into cold air aloft intensifying thunderstorm activity). In addition, mid-latitude dynamics are playing a role…the approaching frontal system and associated upper-level trough of low pressure approaching Ophelia is giving the system a “poleward outflow jet” to pull air away from the system and allow the surface low to strengthen.

us_sat-en-087-0_2017_10_14_16_15_15827_127
Meteorological Analysis of Category 3 Hurricane Ophelia. Favorable dynamic and thermodynamic set up allowing system to strengthen at high latitude, over cooler waters for hurricane maintenance. With that said, water temps under Ophelia are running 2-3 degrees C above normal, also allowing it to have its unusual intensity near Western Europe.

See my previous post from late last night for my wind forecast for Ireland. Strong winds should begin to impact the island midday Monday (local time), with stormy conditions lasting into Monday night. The southeastern Azores will see some gusty winds and 1-3 inches of rain as it passes by this evening and night.

–Meteorologist Nick Humphrey

Analysis and Forecast Impacts of Post-Tropical Ophelia in Ireland Monday

Hurricane Ophelia is a high-latitude hurricane by tropical standards…a Category 2 storm with maximum sustained winds of 100 mph as of 11 pm AST…moving south of Azores at 20 mph.

Analysis
Analysis of meteorological state around Hurricane Ophelia at 2 am AST. The hurricane is moving south of the Azores island chain and will pass between the Azores and Portugal Sunday morning.

This hurricane, is on track to take its already unusual path northward toward a collision course with Ireland and the United Kingdom Monday and Tuesday!

023933_5day_cone_no_line_and_wind
National Hurricane Center advisory on Ophelia and it’s path. It’s expected to reach Ireland as a “post-tropical” cyclone…a hybrid frontal system…on Monday. VERY rarely are tropical cyclones, particularly any stronger than Category 1 located in the Northeast Atlantic Ocean.

Not to worry, however. Ophelia will NOT be a tropical cyclone when it arrives in the British Isles Monday. Sunday, the hurricane will begin to pass over much cooler waters between the Azores and Portugal (and note, the hurricane is currently over waters 2-3 degrees C/~3.5-5.5 degrees F above normal). At the same time, if you look at the previous satellite analysis, the hurricane will begin to interact with the existing frontal zone and ingest air from an approaching cold air mass moving in from the North Atlantic. This will begin the process of extratropcial transition where Ophelia becomes a mid-latitude frontal system. However, because of its old, warm tropical air mass, it will continue to retain some of its internal energy, enabling it to be a powerful hurricane-force windstorm.

us_model-en-087-0_modez_2017101400_60_1642_149
European “Euro” Model showing Post-Tropical Cyclone Ophelia approaching Ireland Monday morning (AST). Other global computer models vary the center of circulation either just offshore the west shore of Ireland or make landfall over southern Ireland Monday morning.
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Euro Model showing damaging wind gusts overspreading Ireland from south to north Monday. Models generally agree with bringing damaging wind gusts of 75-85 mph (~120-135 km/h) to the south and southwest coast of Ireland Monday afternoon (local time) with isolated gusts over 100 mph (~160 km/h). Gusts to 60-65 mph (97-105 km/h) with isolated higher gusts to 75 mph (120 km/hr) in the south of the island will be possible across much of the rest of the country into Northern Island Monday evening and night. All surrounding coastal waters will be hazardous for marine interests.

I have moderate confidence in my forecast…some uncertainty deals with the track of the low pressure system. A track farther offshore to the west would limit significant winds to the south and west shores and coastal communities. A track very close or even onshore the south coast would send very high winds deeper inland into Ireland. Regardless, those in the country should expect widespread downed trees, power outages, and difficult driving conditions for high-profile vehicles during the afternoon into late evening Monday.


Here is the climatological history of all known tropical cyclones in the North Atlantic just to show the rarity of systems such as Ophelia. Although some cyclones may have been missed prior to the satellite area, it is possible that such cyclones were less likely to survive in the distant past because of cooler waters where Ophelia is located now. Sea surface temperatures have warmed on Earth because of climate change.

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All hurricane tracks in the North Atlantic (1851-2012). Note, tracks heading to near the British Isles were likely as extratropical systems. Hurricane Vince, however, made a historic landfall as a tropical depression in southern Spain in October 2005.
GFS-025deg_NH-SAT2_SST_anom
Ophelia is over waters 2-3 degrees C above normal. The hurricane will move away from waters favorable for hurricane maintenance during the day Saturday.

–Meteorologist Nick Humphrey

Hurricane Nate and Dangerous Storm Surge Heading for the Northern Gulf Coast Saturday (Updated at 2 pm CDT)

Update at 2 pm CDT:

Hurricane Nate is likely to be a Cat 1 or 2 at landfall (thinking NHC forecast of 2 as high-end). It is leveling off based on current satellite presentation as well as air force reconnaissance observations. STORM SURGE REMAINS THE GREATEST HAZARD. The asymmetric structure…a product of Nate’s forward motion, may intensify/focus surge/battering waves from Mouth of Mississippi River to the MS/AL border. 9-11 ft surge with battering waves expected Mouth of Miss. River to MS/AL border as center passes nearby. 6-9 ft east to AL/FL border. Dangerous. High tide along Gulf Coast of MS around midnight, passage of center may be 8-10 pm CDT…partial enhancement could exacerbate flooding.

Probability of Cat 1 at initial landfall: 90%

Probability of Cat 2 at initial landfall: 10%

Landfall should be between 5-7 pm in far Southwest Louisiana.

——————-

Hurricane Nate is headed for a likely landfall with the northern Gulf Coast of the US this evening. The hurricane is blasting north-northwestward very fast for a tropical cyclone…26 mph at the moment. This is under the influence of an approaching upper-level trough of low pressure which will eventually turn it northeastward after landfall. The system has continued to organize as expected over the warm waters (83-84 degrees F) and favorable low wind shear. The storm (at 10 CDT) is a Category 1 hurricane with maximum sustained winds of 90 mph with gusts to 110 mph.

vis-animated
Visible imagery of Nate showing its rapid forward motion toward the coast.

The waters atmospheric and oceanic conditions should remain favorable for intensification up until landfall. Landfall is likely between 6-8 pm in far southwest Louisiana. My assessment based on this on trends, is that Nate is likely (65%) to make landfall as Category 2 (100-110 mph sustained) with a moderate chance (10%) to make landfall as a Category 3 (115 mph+), if more rapid intensification occurs during the next 7-8 hrs. There is also a 25% chance of a landfall as a Category 1.

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National Hurricane Center track forecast at 10 am CDT Saturday.

Heavy rainfall (lessened by the storm’s forward speed) is most likely over southern Mississippi into Alabama. Much of Louisiana will miss the worst of the storm, including New Orleans, however points east will face potentially significant surge. Surge may reach 7-11 ft along the mouth of the Mississippi River to the Mississippi/Alabama border; 6-9 ft from the MS/AL border to the AL/FL border, including Mobile Bay.

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Potential Storm Surge Flooding by Nate Saturday night. Orange and Red colors represent potential for 6-9+ feet of surge.

If you know anyone in these areas, please tell them to evacuate NOW!! This storm is moving FAST and storm surge will, BY FAR be the greatest danger from Nate. Far more than the wind or even inland flooding. I do have some concern that the combination of the relatively recent development of this system, its fast forward movement, and resulting shorter lead time, in addition to the system being relatively weaker in terms of maximum sustained winds that people may not leave or leave fast enough. People need to leave and be safe.

I will have updates when possible this afternoon and evening.

Potential Impacts by Tropical Storm Nate this Weekend

Tropical Storm Nate, which developed as a depression yesterday, made landfall in Nicaragua this morning and is moving over eastern Nicaragua and Honduras this evening. Very heavy rainfall and flash flooding has already resulted in 22 deaths in Nicaragua and Costa Rica.

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Heavy showers and thunderstorms producing heavy rain over portions of Central America from Tropical Storm Nate this evening and into tonight. (image valid at 5:15 pm CDT).

Nate is progressing generally northward and will emerge over the Northwest Caribbean Sea late tonight where it will have an opportunity to reorganize. The waters over that region are running in the range of 84-86 degrees F (29-30 degrees C), more than sufficient for re-intensification. With that said, the inner core will likely be badly “gutted” by the mountainous terrain of Nicaragua and Honduras and with a second landfall possible Friday evening, time will likely be limited for more robust intensification. With that said, minimal hurricane strength is possible, with a lower chance that the storm may get stronger if it’s inner core can re-organize quickly Friday.

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National Hurricane Center forecast (issued 5 pm EDT Thursday) showing a likely landfall on the Yucatan Peninsula of Mexico Friday evening and likely US impacts on the northern Gulf Coast beginning Saturday evening.

A Hurricane Watch and Tropical Storm Warning is in effect for much of the coastal Yucatan Peninsula. Again, the major threats will be from water…heavy rain and freshwater flooding and also modest (although still hazardous) storm surge and high wave action.

Potential Impacts for Central Gulf Coast of US-

While many details are still in need of being honed in for the Central Gulf Coast…it is highly likely a tropical storm or minimal hurricane will approach the region Saturday evening with landfall early morning Sunday. The biggest threats will be from water (flooding/surge) with wind producing damage from falling trees and power outages.

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NWS Weather Prediction Center 5 day accumulative rainfall forecast (valid beginning 7 pm CDT Thursday) showing heavy rainfall along the track of Nate and its remnants expected, particularly Saturday afternoon into early next week. Very heavy rainfall possible in Greater New Orleans area which is prone to freshwater flooding.

Sea surface temperatures are slightly cooler along the northern Gulf Coast north of the Loop Current (82-84 degrees F/28-29 degrees C). Still more than warm enough for intensification if the system can remain over the current (a slightly farther west track may leave it over slightly cooler waters longer).

SSTs
Analysis of Sea Surface Temperatures and the Loop Current. Nate will track along the Loop Current much of its track over water, providing with fuel to re-intensify. (Analysis by Earth Nullschool).

Also, given the shear currently over the Central Gulf will relax over the next couple of days (as an area of upper-level high pressure over Texas shifts westward and weakens), Nate will have an opportunity to re-intensify over the Gulf after leaving the Yucatan Peninsula. Computer models have some variability in timing of an upper trough which will move over the US Central Plains during the day Saturday. This will ultimately influence the exact track of the center of Nate. However both deterministic and ensemble members of the various models depict a likely landfall of the center somewhere from Southeast Louisiana to coastal Mississippi/Alabama. Regardless, widespread heavy rain (particularly near and east of the center), moderate storm surge flooding and high wind conditions will be likely over the coastal areas of these states by Saturday afternoon, spreading inland Saturday night and Sunday. Tropical storm force winds (sustained 39 mph+) will likely arrive on the LA Coast Saturday evening.

 

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Earliest Reasonable Arrival Time for Tropical Storm-Force (issued 5 pm EDT). Folks along the Central Gulf Coast should have preparations for stormy conditions completed by Saturday afternoon.

Tropical cyclone watches will likely be issued for portions of Louisiana, Mississippi and Alabama late tonight or early tomorrow morning.

Climatology Update-

The Atlantic Hurricane Season is currently running above normal (1966-2010 norms in parenthesis): 14 named storms (9), 8 hurricanes (6) and 5 major hurricanes (2). In terms of Accumulated Cyclone Energy (a function of maximum sustained winds over time), 2017 ranks (as of this post) as the 6th most active season on record for the North Atlantic Basin. The average temperature of the North Atlantic Main Development region (open tropics west of Africa) exceeded 83 degrees F (~28 degrees C) for the 9th time since 2002 (had never done so in the record prior going back to 1981). The MDR is the 3rd warmest on record overall.

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Global Climate Change and its Potential Connection to Hurricane Activity (cited research)

Because of recent North Atlantic Hurricane Season activity…many people have questioned whether hurricanes are becoming stronger and more numerous because of climate change. In the social media universe, I’ve seen many opinionated debates within the general public, as well as meteorologists and perhaps a few sprinkling of climatologist opinions here and there. Not to mention, interesting statements from non-climate scientists. What I have not seen much, however, is any discussion of peer-reviewed research on the topic. There’s so much knowledge being gathered every year by scientists trying to answer important questions about our past, present and future. How climate change will impact regional weather and climates is one of the most important questions because of potential impacts to people, agriculture and natural resources.

I decided to do a (very brief) search of literature on science’s current understanding of climate change as it relates to tropical cyclones. I looked into both the potential connection of global warming to these events in the current climate (attribution), as well as projections for these events based on the “business-as-usual” scenario for carbon dioxide emissions, which is a high emissions scenario and steady increase in CO2 concentration. Research cited are just a sampling of what’s out there and what I looked over. Here are some themes I found interesting (takeaway statements at the end):

Climate models* appear to show a signal toward more intense (Category 4-5 Saffir-Simpson) tropical cyclones overall in the world by the latter half of the 21st century. However, there is also a potential for a downward trend in cyclone numbers in many basins (see #1-4).

The decrease in overall cyclone numbers by the second half of the century is thought to be a product of increasing vertical wind shear over tropical oceans limiting weaker storms. However, many researchers expect there to be a significant upward trend in more intense storms (Category 4-5) as the oceans continue to warm and tropical cyclone formation and track density moves poleward. So formerly less favorable sub-regions of basins may see an overall increase in cyclone activity (with more storms which will be stronger than before in those regions) and in the increasingly less hospitable regions (over the long term), storms which do form when conditions are favorable on short time scales may see cyclones which are also more intense than in years past.

As for historical conditions leading to the present…there does not appear to be a conclusive signature by global warming on tropical cyclone intensity outside of natural variability on a global scale (3-4). However, some regional signals related to frequency changes are being actively studied. 

There is some suggestion (4) based on modeling past climate change to the present time that warming (which would enhance the potential intensity for hurricanes) has been muted by the industrial production of aerosols (particulates like sulfates and nitrates), which actually reflect sunlight from reaching Earth’s surface. However, as warming continues into mid-century, its effect of trapping heat will begin to significantly exceed aerosol cooling effects leading to the more pronounced impacts on cyclone intensity stated earlier (unless CO2 emissions are significantly reduced soon). So while global warming is happening in the background, hurricane potential intensity as we currently witness it is likely still being dominated by natural cycles. (For more on climate change research into tropical cyclones, you can also see this webinar done by climate change researcher Dr. Kerry Emanuel for Climate Central).

With that said, some researchers see signs of a global warming signature associated with recent increased tropical cyclone *frequency* in sub-regions of basins. These include the far eastern portion of the North Atlantic Basin (4), close to the East Asian Coast (5), and a portion of the North-Central Pacific Basin (6). Research is still ongoing on global warming’s past and future influence on activity in individual tropical cyclone basins.

Meanwhile, there is evidence of other impacts related to tropical cyclones (and other significant weather phenomena) and climate change. These include higher rainfall rates (7) and higher storm surge related to sea-level rise from the melting polar ice sheets and thermal expansion of the oceans (8). In addition, there is some scientific evidence that tropical cyclones in recent decades have begun to intensify more rapidly because of increased ocean warming (9). And while not completely clear yet whether it is fully tied to climate change, it is known that the observed North Atlantic Power Dissipation Index (PDI) has increased significantly since the mid-1970s (10; positively correlated to sea surface temperatures) and globally, the strongest tropical cyclones in respective basins have grown stronger since 1981 (Elsner et al, 2008…not included here). Note that scientific critics point out the use of observational data with differences in quality – satellite intensity estimates and reconnaissance flights (or lack of them) – over recent decades could put some uncertainty in these results.

My thoughts? Although inconclusive, possible intensity signals may be a hint of the projected effects of climate change as PDI and high-end cyclone intensity are highly correlated to sea surface temperatures. SSTs are increasing from global warming and this would connect with what climate models suggest of future tropical cyclone activity, if these historical trends are, in fact partially related to climate change.

The Takeaways:

  1. Tropical cyclone intensity at the highest end of the scale appears likely to increase through the 21st century because of climate change, especially if human civilization does not significantly reduce greenhouse gas emissions soon.
  2. While a current climate change signal to intensity is difficult to detect and still a matter of debate, storms in recent decades appear to be intensifying faster, are capable of producing more extreme precipitation events and higher storm surges because of rising sea levels caused by ice sheet melting and thermal ocean expansion. There also appears to be some detectable changes in frequency of storms within individual basins which may locally enhance risk.
  3. Regardless of the exact changes in frequency and intensity of tropical cyclones, the risks to individuals and society because of climate change will increase into the coming decades. It will be important for people and governments to make decisions (beyond greenhouse gas emissions) related to property, coastal land use and emergency management policy to mitigate increasing tropical cyclone hazards, particularly from water (storm surge/inland flooding).

Note: It is of EXTREME importance that those with a desire to communicate climate change issues try to inform our fellow citizens to the best of our ability. Climate change is one of the important issues facing our world (the impact on the global food supply and human health may be actually of greatest importance, but rarely discussed as those aren’t “sexy” topics…). People have their thoughts on the issue based on experiences, politics, religious/spiritual beliefs, etc. However, at the end of the day, we must inform and connect what we know to people’s concerns and allow people to decide as they may. Without censorship (“We can’t discuss climate change right now!”) or nonsensical exaggerations (“So many hurricanes, it’s a new era of superstorms!”). Stay informed (give informed opinions) and tell people why they should care as it relates to their lives. Like everything else we should communicate to the concerns of people. Considering most Americans are now, in fact, concerned about climate change, there’s really NO excuse not to discuss the issue in a serious, informed manner if we have the interest to discuss it at all.


Additional Note: *-Climate models are not weather forecast models. They do not forecast the atmosphere using initial conditions, but take a climate state (for example, our current climate) and adjust “forcings” on the climate system (carbon dioxide emissions for example). The effect of these changes to “boundary conditions” over time are interpreted for land, sea, the cryosphere and (for Earth System models), the biosphere. Global climate is based on thermodynamic and hydrologic balances which will look for equilibrium when changes to a part of the system are applied. (For more on climate models you can see this webinar by Research Meteorologist Keith Dixon of NOAA’s Geophysical Fluid Dynamics Laboratory for Climate Central).

References (links are PDFs):

#1 – Bell et al. (2013)

#2 – Murakami et al. (2011)

#3 – Wang and Wu. (2013)

#4 –  Sobel et al. (2016)

#5 – Cheng-lin et al. (2016)

#6 – Murakami et al. (2015)

#7 – Knutson et al. (2013)

#8 – Jevrejeva et al. (2016)

#9 – Kishtawal et al. (2012)

#10 – Emanual (2005)

—Meteorologist Nick Humphrey